Relationship between the sound speed ratio of the compressional wave and the physical characteristics of seafloor sediments

The acoustic characteristics of seafloor sediments are complicated and diverse, due to their complex components and structures. A variety of theoretical interpretation model has many parameters and each has its own applicability. By using volume averaging method and equivalent parameter method, we researched the acoustic propagation mechanism of seafloor sediment, and proposed a general model of sound speed ratio of compressional wave of sediment against bottom seawater(GMSSR) with less parameter. The GMSSR contained four physical parameters including elastic structure distribution factor, porosity, equivalent density ratio and equivalent elastic modulus ratio. With the analysis of two limit states of the structures of two-phase medium of seafloor sediment: series structure and parallel structure, an equivalent elastic modulus expression of seafloor sediments under normal circumstances was established with the introduction of elastic structure distribution factor and series-parallel structure of volume averaging distribution.The GMSSR was applied to analyze the generality of empirical models and the scattering of measurement datasets of surficial seafloor sediment in different sea reasonably. The analysis showed that:(1) the surface sediment is mainly with series structure, being close to the suspension state or with little accumulation condition of parallel volume components;(2) the influence of equivalent elastic modulus ratio factor is greater than the equivalent density ratio. The structure change is often affecting the distribution of elastic structure to change the equivalent elastic modulus ratio, resulting in the change of sound velocity;(3) the different empirical equations in different study sea areas between sound speed ratio and porosity are similar and can be explained by the GMSSR;(4) the large dispersion of measurement sound speed ratio of surficial seafloor sediments in South China Sea can be reasonably interpreted by the difference of elastic structure distribution factor.